Much cargo is shipped in large containers that are 20 to 40 feet long on ocean going vessels from one country to another. These containers have two doors on one end that are locked by locking bars that are secured into female locking receptacles in the frame of the container above and below the doors. A container door cannot be opened without unlocking the bar on that door and sometimes the bar on the other door as well. One door frequently overlaps the other door, in which case, only a bar is needed on the overlapping door. These containers are subject to pilferage, smuggling and acts of terrorism by unauthorized people opening the container after it has been locked at the point of origination of the shipment. When these containers are moving from one country to another, they frequently are inspected by custom officials before leaving the country of origin. They may also need to be inspected by customs officials upon entry into the country of final destination of the cargo. Because of the vast quantity of goods that are being shipped in these containers, these inspections by customs authorities and other government officials are expensive and time consuming and, consequently sometimes lack in thoroughness. It would be highly desirable to have a security system that could be activated by a customs official in the country of origin that would clearly identify whether the container had been opened or not to a custom official in a country through which the container is passing, or to a custom official in the country of final destination. These containers frequently pass from one shipper to another until they reach their final destination. Regardless of any inspections by customs officials, these shippers and the ultimate customer would like to have a security system that would tell them whether the container has been opened or tampered with. This is important not only for containers that go from one country to another, but also for containers that are shipped entirely within a single country. While the containers carrying cargo may not be very expensive, the cargo being carried may be extremely valuable or may be of extreme importance to national security if it contains military goods and the like.
The trailers that are pulled by tractors on the highways have similar doors to those on ocean going containers and are also locked by locking bars. It would be desirable to have a security system for these trailers as well. Even when the goods are not being carried from one country to another, a security system would be very valuable to detect pilferage or the adding of smuggled goods or contraband to the trailer in the unauthorized opening of the trailer.
The locking bars on these containers and trailers frequently have handles that can be locked together by a padlock or by a chain and padlock. In some cases these bars are locked only by a chain and padlock. These padlocks are relatively easy to “pick” and open allowing unauthorized personnel access to the cargo. These padlocks can then be relocked without leaving a trace of the unauthorized entry.